Actuators have been widely used which are configured to attach a slider to a feed nut threadably engaged with a feed screw such as a ball pivotally supported at its ends by bearing members and move the feed nut and the slider as a moving body in an axial direction of the feed screw according to the rotation of the feed screw. In such an actuator, the feed screw is known to resonate, thereby causing a possibility of problems such as noise and the breakage of the feed screw if the number of revolutions of the feed screw (number of revolutions per second) coincides with the natural frequency of the feed screw. Accordingly, in an art disclosed in Japanese Patent Publication No. 3221804, support brackets are moved at half the moving speed of a slider in conjunction with a movement of the slider while a feed screw is supported by the support brackets.